v5.6.1

Nuthatch 5.6.1 gives each watched account its own backfill pace. There is no storage migration.

One slow account no longer slows the rest

The address-history backfill sizes its trace window by how long the last window took, and in 5.6.0
every account shared one pace (#2061). An account whose traces were slow to fetch shrank the window
for every other account in the nest, so a light account was backfilled in the heavy one's small steps
and made far more trace_filter calls than it needed.

Each account now keeps its own pace (#2063), kept across polls and started fresh on a restart. In the
new test, one account pays 400 ms a call and another pays nothing over 99,000 blocks: the cheap
account finishes in at most 30 trace_filter calls, where with one shared pace the test ran past its
120 s limit.

Gated on Lodestar's data

The change is in the address-history path, which no production nest declares, so this release
changes no query path the release gate measures.

Compatibility and upgrade

Replace the binary and restart. A 5.6.0 store is used as it is.